hicAdjustMatrix can mask, remove or keep defined regions from a BED file or given chromosomes.
$ hicAdjustMatrix -m matrix.cool --action keep --chromosomes chr1 -o matrix_chr1.cool
$ hicAdjustMatrix -m matrix.cool --action mask --regions mask_regions.bed -o matrix_masked.cool
mask_regions.bed
chr1 10 30
chr1 50 300